A silver halide photographic material comprises a silver halide emulsion layer provided on a support. The silver halide emulsion is usually chemically sensitized to obtain a desired sensitivity or gradation. Examples of the chemical sensitizer include a sulfur sensitizer, a selenium sensitizer, a tellurium sensitizer, a noble metal (such as gold) sensitizer, a reduction sensitizer and a combination thereof.
For several years there has been a growing demand for improvement of silver halide photography. The recent photographic material requires very high sensitivity. With respect to the obtained image, improvement of the graininess and the sharpness is required. A rapid image forming process such as a quick development process is also required. The sensitization and the sensitizer have been improved to meet these requirements.
The tellurium sensitization and the tellurium sensitizer are disclosed in U.S. Pat. Nos. 1,623,499, 3,320,069, 3,531,289, 3,655,394, 3,772,031 and 4,810,626, U.K. Patents No. 235,211, No. 1,121,496, No. 1,295,462 and No. 1,396,696, and Canadian Patent No. 800,958.
Canadian Patent No. 800,958 at page 2 discloses various tellurium sensitizers, which include colloidal tellurium metal; aliphatic isotellurocyantates; alkali metal, alkaline earth or ammonium salts; aliphatic telluroureas; and telluroketones. These tellurium sensitizers disclosed in Canadian Patent No. 800,958 are excellent in sensitivity, antifogging property and gradation. Canadian Patent No. 800,958 further describes that the sensitivity is greatly improved when the tellurium sensitizer is used in combination with a noble metal sensitizer.